Go to Bulletproofme.com. Know most of these plates are made by the same mfg.'s. Unless you're gonna drop $2000+ for plates and $1500+ for side plates, medium sizes and are very light and rated in excess of Lvl.4 for the best ones, then I'd get a good set of standard or even "light" (the extra cost vs. weight drop is worth it for these, it's what I have) ceramic stand alone Lvl.4 plates. They'll be worth it and if you ever want to use a lighter plate carrier, these'll work without the soft armor. These plates have been tested on videos on YouTube and some members of some other sites also duplicated the results. These plates are generally one use items. Once shot, they need to be replaced. Some perform better than others after being hit. What that 10x12 stand alone plate took was impressive, you should look it up.
There are ultralight 1" thick Lvl.4 poly plates now. Plastic. Don't know much about 'em.
Difference in the ceramic plates is generally the different ingredients --some use aluminums, I hear some are playing with carbon fiber. You can call Bulletproofme.com and they'll tell you the differences. Some give better performance than others, but most are just heavier or lighter, depending. Military plates have a padding wrapped around them before they wrap 'em in canvas. They're thicker than the plates that you buy from Bulletproofme.com that don't have that, and if worried about wear due to sharp edges (being tight is just a liability of fitting loose because they move and that causes wear; in addition, loose plates won't provide the same coverage as one that's snug --body armor is supposed to worn snugly). All you need do is wrap 'em yourself --I used bubblewrap and tape IIRC. Light and it works and can be replaced when you clean.
Their plates are SAPI cut. ESAPI isn't a cut, just an upgrade of the SAPI plate. In a nutshell, SAPI was black and ESAPI was green and they had stickers that told what they were on back. I have a pair, problem with used ESAPI plates is that soldiers are rough on gear, and there's a crack right down the middle of one. The wrapping holds it together well, but you can definitely feel it. They get dropped, you lay down with your gear against something hard, whatever. In some ways it's like wearing a dinner plate for armor in terms of fragility, but take care of them and they'll stop rounds if need be.
I have a Paraclete RAV07 (I think it's that one) and Paraclete makes some of the best vests and carriers I've seen. I love mine. Much better than any issue armor I've used.
There are other trustworthy sellers of plate armor, just be sure they have a good reputation regarding the armor they sell. Bulletproofme.com has good stuff for good prices. Used plate that hasn't been x-rayed (which is about as much as the plates are worth used) then they should be looked over, a new plate is better IMO/E. If you have a good set of issue ESAPI and didn't pay much for 'em, then that's fine, just make sure the corners aren't broken or crumbled and there isn't a crack or break you can feel, but without an x-ray there is just no way of knowing.
Having a cummerbund, a good wide one inside of the vest as well as an external one, goes a LOOONG way towards comfort, which translates to more effective gear. Doesn't hang 70lbs. of shit on your shoulders, it balances it out on your hips and waist. Very nice. The IOTV had this upgrade vs. the OTV, was one of the big changes I noticed right away, and usually quality brands will use these.
Good luck.
